NUMERICAL ESTIMATE. 



41 



as well as in their tendency to admit those of doubtful 

 claim; but they are sufficiently near to each other on 

 these points to admit of comparison numerically. The 

 following list presents the number of species contained in 

 each of them : — 



Maritime 



No. 



Inland. 



No. 



Devon 



Yarmouth 



Anglesea - 



Berwick 



Edinburgh 



Glasgow 



Mean 



774 

 724 

 764 

 707 

 774 

 629 



Tonbridge 



Oxford 



Bedford 



Cambridge 



Bath 



Lanark 



Mean 



717 

 727 

 717 

 847 

 632 

 604 



728f 



™-£ 



One investigating the flora of a limited area, as a radius 

 of ten or twenty miles, in Britain, may judge of his suc- 

 cess by the above. The flora of Northumberland and 

 Durham, 1026 species (Trans. Nat. Hist. Soc. of New- 

 castle, quoted in Edin. Journ. of Nat. and Geog. Science), 

 is considerably above the mean, after allowing for the 

 greater extent of surface ; while that of Southport in 

 Lancashire, 392 species (Hist, of Southport), is as much 

 too low. The latter, however, probably relates to a 

 small area, while the former is augmented by many species 

 brought in shipping to the ballast-hills near Newcastle. 

 The Flora of Bath does not include the genus Salix, and 

 refers to a circumscribed space. I believe the average 

 number of species contained in a score of Manuscript 

 Catalogues of plants found in particular counties or 

 vicinities, procured from friends or correspondents, will 

 not amount to 600 ; but several of such catalogues en- 

 tirely omit some genera, and do not profess to be com- 

 plete lists of certain orders, as Gramineae, Cyperaceae, and 

 Amentaceae. On the average, a single county appears to 

 contain nearly one half the whole number of species found 



